1. Technical Field
The present invention relates to an ink jet printer, and more particularly a method for cleaning the nozzle of an ink cartridge mounted in an ink jet printer.
2. Related Art
Generally, an ink jet printer includes a carrier motor for driving an ink cartridge provided with a print head. The ink cartridge is driven by a timing belt carried on a driving pulley rotated by the carrier motor. Thus, the ink cartridge is driven by the carrier motor.
Such arrangements are disclosed in the following patents: U.S. Pat. No. 4,050,075 to Hertz et al., entitled Ink Jet Method And Apparatus, U.S. Pat. No. 4,433,341 to Thomas, entitled Ink Level Control For Ink Jet Printer, U.S. Pat. No. 5,448,274 to Hirabayashi et al., entitled Ink Jet Recording Apparatus And Carriage Mechanism Therefor, U.S. Pat. No. 5,451,987 to Perrin, entitled Ink Circuit Particularly Intended To Pressurize A Pigment Ink For An Ink Jet Printer, U.S. Pat. No. 4,456,916 to Kocot, entitled Ink Jet Cartridge With Hydrostatic Controller, U.S. Pat. No. 4,527,175 to Kojima et al., entitled Ink Supply System For Nonimpact Printers, and U.S. Pat. No. 4,577,197 to Crean et al., entitled Ink Jet Printer Droplet Height Sensing Control.
In ink jet printers, the ink cartridge contains pigment ink which consists of a pigment and liquid. The pigment ink is jetted out through the nozzle of the print head of the cartridge during a print operation or when cleaning the nozzle. The cleaning of the nozzle is such that, when the power is on, the pigment ink within the nozzle is jetted out so as to prevent the nozzle from clogging. When cleaning the nozzle, the jetted amount of the pigment ink is usually 100-200 drops.
The weight of the pigment ink is heavier than that of the liquid. Therefore, when the power is off, or when power is left on without printing, the pigment part of the pigment ink settles to the bottom.
When considering the pigment part sunk to the bottom of the ink cartridge, the lower part of the ink cartridge is occupied by pigment deposited on the bottom, and the upper part is occupied by the liquid serving as the carrier. Hence, in this state of the cartridge, if the pigment ink is jetted out to print or clean the nozzle, more pigment is contained in the jetted portion of the pigment ink than is the case in the normal state of the cartridge because the print head is mounted on the lower part of the cartridge. If the printing or nozzle cleaning operation is repeated in this state, the density of the pigment becomes thinner, that is, the pigment content is reduced. Accordingly, the quality of the printed images deteriorates, resulting in an early replacement of the ink cartridge. Furthermore, when the pigment is deposited to the bottom, the print head can not perform the printing and nozzle cleaning operations normally because of insufficient carrier liquid, making the nozzle clog.
Elaborate and expensive solutions to this problem have been proposed. For example, previously mentioned U.S. Pat. No. 5,451,987 to Perrin provides magnetic agitators at the base of reservoirs to prevent settling of pigment. However, such an arrangement complicates matters and adds unnecessary expense to the cost of manufacturing the ink-jet printer.